In recent years, there has been an increasing interest in the use of ceramics for structural applications historically served by metals. The impetus for this interest has been the superiority of ceramics with respect to certain properties, such as corrosion resistance, hardness, modulus of elasticity, and refractory capabilities, when compared with metals.
Current efforts at producing higher strength, more reliable, and tougher ceramic articles are largely focused upon (1) the development of improved processing methods for monolithic ceramics and (2) the development of new material compositions, notably ceramic matrix composites.
A composite structure is one which comprises a heterogeneous material, body or article made of two or more different materials which are intimately combined in order to attain desired properties of the composite. For example, two different materials may be intimately combined by embedding one in a matrix of the ether. A ceramic matrix composite structure typically comprises a ceramic matrix which incorporates one or more diverse types of filler materials such as particulates, fibers, rods, and the like.
There are several known limitations or difficulties in substituting ceramics for metals, such as scaling versatility, capability to produce complex shapes, satisfying the properties required for the end use application, and costs. Several copending patent applications assigned and issued Patents to the same owner as this application (hereinafter referred to as Commonly Owned Patent Applications and Patents), overcome these limitations or difficulties and provide novel methods for reliably producing ceramic materials, including ceramic composite materials. The method is disclosed generically in Commonly Owned U.S. Pat. No. 4,713,360, entitled "Novel Ceramic Materials and Methods for Making Same", which issued on Dec. 15, 1987, from U.S. patent application Ser. No. 06/818,943, filed Jan. 15, 1986, which was a continuation-in-part of application U.S. Ser. No. 06/776,964, filed Sep. 17, 1985, and now abandoned, which was a continuation-in-part of application Ser. No. 06/705,787, filed Feb. 26, 1985, and now abandoned, which was a continuation-in-part of application Ser. No. 06/591,392, filed Mar. 16, 1984, and now abandoned, all in the names of Marc S. Newkirk et al. This Patent discloses a method of producing self-supporting ceramic bodies grown as the oxidation reaction product of a molten parent precursor metal which is reacted with a vapor-phase oxidant to form an oxidation reaction product. Molten metal migrates through the formed oxidation reaction product to react with the oxidant, thereby continuously developing a ceramic polycrystalline body which can, if desired, include an interconnected metallic component. The process may be enhanced by the use of one or more dopants alloyed with the parent metal. For example, in the case of oxidizing aluminum in air, it is desirable to alloy magnesium and silicon with the aluminum to produce alpha-alumina ceramic structures. This method was improved upon by the application of dopant materials to the surface of the precursor metal, as described in Commonly Owned U.S. Pat. No. 4,853,352, entitled "Methods of Making Self-Supporting Ceramic Materials and Materials Made Thereby", which issued on Aug. 1, 1989, from U.S. patent application Ser. No. 07/220,935, which was a Rule 62 continuation of commonly owned U.S. patent application Ser. No. 06/822,999, filed Jan. 27, 1986, and now abandoned which was a continuation-in-part of Ser. No. 06/776,965, filed Sep. 17, 1985, and now abandoned, which was a continuation-in-part of Ser. No. 06/747,788, filed Jun. 25, 1985, and now abandoned, which was a continuation-in-part of U.S. Ser. No. 06/632,636, filed Jul. 20, 1984, and now abandoned, all in the names of Marc S. Newkirk et al.
This oxidation phenomenon was utilized in producing ceramic composite bodies as described in Commonly Owned U.S. Pat. No, 4,851,375, entitled "Methods of Making Composite Ceramic Articles Having Embedded Filler", which issued on Jul. 25, 1989, from U.S. patent application Ser. No. 06/819,397, filed Jan. 17, 1986, which was a continuation-in-part of U.S. Ser. No. 06/697,876, filed Feb. 4, 1985, and now abandoned, all in the names of Marc S. Newkirk et al. and entitled "Composite Ceramic Articles and Methods of Making Same". These patent applications and patents disclose novel methods for producing a self-supporting ceramic composite by growing an oxidation reaction product from a parent metal into a permeable mass of filler, thereby infiltrating the filler with a ceramic matrix. The resulting composite, however, has no defined or predetermined geometry, shape, or configuration.
A method for producing ceramic composite bodies having a predetermined geometry or shape is disclosed in Commonly Owned and Copending U.S. Pat. No. 5,017,526, entitled "Method of Making Shaped Ceramic Composite", which issued on May 21, 1992, from U.S. patent application Ser. No. 07/338,741, filed Apr. 14, 1989, as a Rule 62 Continuation of U.S. patent application Ser. No. 06/861,025, filed May 8, 1986, and now abandoned, in the names of Marc S. Newkirk et al. and entitled "Shaped Ceramic Composites and Methods of Making the Same". In accordance with the method in U.S. Pat. No. 5,017,526, the developing oxidation reaction product infiltrates a permeable preform of filler material in the direction towards a defined surface boundary.
It was discovered that high dimensional fidelity is more readily achieved by providing the preform with a barrier means, as disclosed in Commonly Owned U.S. Pat. No. 4,923,832, which issued on May 8, 1990, from U.S. patent application Ser. No. 06/861,024, filed May 8, 1986, in the names of Marc S. Newkirk et al. and entitled "Method of Making Shaped Ceramic Composites with the use of a Barrier". This method produces shaped self-supporting ceramic bodies, including shaped ceramic composite bodies by growing the oxidation reaction product of a precursor metal to a barrier means spaced from the metal for establishing a boundary or surface.
Ceramic composite bodies having a cavity with an interior geometry inversely replicating the shape of a positive parent metal mold or pattern are disclosed in Commonly Owned U.S. Pat. No. 4,828,785, entitled "Inverse Shape Replication Method of Making Ceramic Composite Articles", which issued on May 9, 1989, from U.S. patent application Ser. No. 06/823,542, filed Jan. 27, 1986, in the names of Marc S. Newkirk, et al. and entitled "Inverse Shape Replication Method of Making Ceramic Composite Articles and Articles Obtained Thereby", and in Commonly Owned U.S. Patent No. 4,859,640, which issued on Aug. 22, 1989, from U.S. patent application Ser. No. 06/896,157, filed Aug. 13, 1986, in the name of Marc S. Newkirk and entitled "Method of Making Ceramic Composite Articles with Shape Replicated Surfaces and Articles Obtained Thereby".
The above-discussed Commonly Owned Patent Applications and Patents disclose methods for producing ceramic and/or ceramic composite articles which overcome some of the traditional limitations or difficulties in producing ceramic articles as substitutes for traditional ceramics and metals in various end-use applications.
Common to each of these Commonly Owned Patent Applications and Patents is the disclosure of embodiments of a ceramic body comprising an oxidation reaction product interconnected in one or more dimensions (usually in three dimensions) and, if desired, a metallic component comprising one or more metallic constituents. The volume of metal, which typically includes non-oxidized constituents of the parent metal and/or metal which has been donated by (e.g., reduced from), for example, an oxidant, a filler or some constituent added to a filler, depends on such factors as the temperature at which the oxidation reaction product is formed, the length of time during which the oxidation reaction is allowed to proceed, the composition of the parent metal, the presence of dopant materials, the presence of reduced constituents from any source, etc. Some of the metallic constituents can be isolated or enclosed, but also a substantial volume percent of metal can be interconnected and accessible, or rendered accessible, from an external surface of the ceramic body. It has been observed for these ceramic bodies that this metal-containing component (both isolated and interconnected) can range from about 1 to about 40 percent by volume, and sometimes higher, if desired. The metallic component can impart certain favorable properties to, or improve the performance of, the ceramic articles in many product applications. For example, the presence of metal in the ceramic structure may have a substantial benefit with respect to imparting fracture toughness, thermal conductivity, or electrical conductivity to the ceramic body.
The entire disclosures of all of the foregoing Commonly Owned Patent Applications and Patents are expressly incorporated herein by reference.